When capturing an image of an object illuminated by an incandescent light bulb, fluorescent lamp, or other light source by using an imaging apparatus which has a CCD (charge coupled device) or other imaging element mounted therein, sometimes a striped pattern of light and shade is formed in the captured image and it is difficult to discriminate what the object is.
This is because, in contrast to an interlace type imaging apparatus wherein a field frequency is generally about 60 Hz, a modulation frequency of a light source is about 100 Hz or 120 Hz, so there is a deviation in the image capturing timing depending on the commercially available power supply frequency (50 Hz or 60 Hz).
In order to solve such a problem, for example, an imaging apparatus shown in PLT 1 is disclosed. In the art described in this PLT 1, the imaging apparatus captures an image of the object with a higher frame rate than the modulation frequency of the light source.
In this regard, in general imaging apparatuses being circulated on the market, the majority apparatuses are compatible with the NTSC (National Television System Committee) system or PAL (Phase Alternating Line Standard) system. For example, in the NTSC system, by interlace scanning, the field frequency is set to about 60 Hz and the frame rate (frame frequency) is set to 30 Hz.
Accordingly, it is difficult to raise the frame rate as in the imaging apparatus disclosed in PLT 1.
In a detection system described in PLT 2, the luminance of the light source is changed by a predetermined multiple of the scan period of the imaging apparatus, and the imaging apparatus captures the image of the object illuminated by this light source.
Due to this, not only can the object be vividly captured, but it is also not necessary to raise the frame rate itself of the imaging apparatus, therefore use can be made of a general imaging apparatus being circulated on the market.